Dead bolts are well known devices for securing a door against intruders. In general they include a surface mounted assembly for containing a bolt and a striker plate for receiving the bolt. A typical dead bolt is disclosed in U.S. Pat. No. 2,527,413 where the bolt is slidable within a slot in the surface mounted assembly to project into an opening in the striker plate. A similar dead bolt is disclosed in U.S. Pat. No. 2,620,213.
The problem with surface mounted dead bolts is they are mounted on the surface of a door or door jamb by wood screws which have limited gripping power. Usually four screws of less than an inch in length are employed to mount a dead bolt. It is obvious that a person could force the door by applying sufficient force against the bolt, pulling the screw out of the door.
Another type of surface mounted door securing device is disclosed in U.S. Pat. No. 3,674,297, directed to an interior door lock. The lock includes a plate mounted on a door jamb, between the edge of the door and the jamb, and a reciprocating latch which projects into the path of the door. With the door latched, the locking device is supposed to withstand attempted forced entry. This, of course, is not always true, since police reports advise that the screws are often ripped from the jamb, leaving the jamb in splingers.
In U.S. Pat. No. 3,347,581 a built-in latch for a metal door is disclosed. The latch projects through the edge of the door to engage a striker plate on a door jamb. Assuming the jamb is made of metal it would be less likely to yield to force. However, if the jamb is made of wood, the striker plate screws would subject to an applied force.
Obviously, a bolt and door and jamb combination could be built which would withstand attempted forced entry, but the cost of such a door and jamb would add substantially to already rising construction costs. It is also apparent from the rising number of break-ins that the present surface mounted dead bolts are not strong enough to prevent a determined burglar from forcing the bolt. The present invention has for its sole object to provide an inexpensive dead bolt which can be used on existing doors and in new construction.